Stephen J. Sowerby

Methylation sequencing analysis refines the region of H19 epimutation in Wilms tumor.

Differential DNA methylation of the parental alleles has been implicated in the establishment and maintenance of the monoallelic expression of imprinted genes. H19 andIGF2 are oppositely imprinted with only the maternal and the paternal alleles expressed, respectively. In Wilms tumor, a childhood renal neoplasm, loss of the H19/IGF2imprinted expression pattern results in silencing of H19and biallelic expression of IGF2. This was shown to be associated with biallelic methylation of the H19 promoter in the tumor and the adjacent kidney tissue suggesting that epigeneticH19 silencing is an early event in Wilms tumorigenesis. An imprinting mark region characterized by paternal allele-specific methylation has been suggested to reside in a GC-rich region of 400-base pair direct repeats starting at −2 kilobase pairs (kb) relative to the H19 transcription start and extending upstream. The upstream boundary of the potential paternal methylation imprint of the H19 gene has yet to be defined. We sought to define this upstream imprint boundary and investigate whether Wilms tumors with loss of imprinting are biallelically methylated in this imprinting mark region. The analysis of 6.6 kb of new upstreamH19 sequence determined in this study identified a series of the direct 400-base pair repeats that extends to approximately −5.3 kb relative to the transcription start. DNA methylation analyses indicated that the upstream boundary of the potential imprint may coincide with the 5′ end of the direct repeats. We found that Wilms tumors with loss of imprinting are biallelically methylated in theH19 upstream repeat region, and we suggest that pathological methylation in this region is the epigenetic error that initiates H19 silencing.

Chiral Symmetry Breaking During the Self-Assembly of Monolayers from Achiral Purine Molecules

Scanning tunneling microscopy was used to investigate the structure of the two-dimensional adsorbate formed by molecular self-assembly of the purine base, adenine, on the surfaces of the naturally occurring mineral molybdenite and the synthetic crystal highly oriented pyrolytic graphite. Although formed from adenine, which is achiral, the observed adsorbate surface structures were enantiomorphic on molybdenite. This phenomenon suggests a mechanism for the introduction of a localized chiral symmetry break by the spontaneous crystallization of these prebiotically available molecules on inorganic surfaces and may have some role in the origin of biomolecular optical asymmetry. The possibility that purine-pyrimidine arrays assembled on naturally occurring mineral surfaces might act as possible templates for biomolecular assembly is discussed.

THE ROLE OF SELF-ASSEMBLED MONOLAYERS OF THE PURINE AND PYRIMIDINE BASES IN THE EMERGENCE OF LIFE

The experimental evidence for the spontaneous formation and structure determination of two-dimensional monolayers of the purine and pyrimidine bases is examined. The plausibility of such structures forming spontaneously at the solid-liquid interface following their prebiotic synthesis suggests a functional role for them in the emergence of life. It is proposed that prebiotic interactions of enantiomorphic monolayers of mixed base composition with racemic amino acids might be implicated in a simultaneous origin of a primitive genetic coding mechanism and biomolecular homochirality. The interactions of these monolayers with carbohydrates and other derivatives is also discussed.

Molecular mechanics study of hydrogen bonded self-assembled adenine monolayers on graphite

Abstract Molecular mechanics calculations using the Dreiding II force field were applied to self-assembled monolayer configurations of the nucleic acid base adenine adsorbed on graphite surfaces. Energy minimization calculations were used to refine the structures proposed by scanning tunneling microscopy (STM) studies and low energy electron diffraction (LEED), and allowed discrimination between competing models on the basis of final configurations and local minima convergence. This allowed the relative position of the adenine molecules within the unit cell of p2gg symmetry to be inferred.

Fate of prebiotic adenine

Equilibrium adsorption isotherm data for the purine base adenine has been obtained on several prebiotically relevant minerals by frontal analysis using water as a mobile phase. Adenine is far displaced toward adsorption on pyrite (FeS2), quartz (SiO2), and pyrrhotite (FeS), but somewhat less for magnetite (Fe3O4) and forsterite (Mg2SiO4). The prebiotic prevalence of these minerals would have allowed them to act as a sink for adenine; removal from the aqueous phase would confer protection from hydrolysis as well, establishing a nonequilibrium thermodynamic framework for increased adenine synthesis. Our results provide evidence that adsorption phenomena may have been critical for the primordial genetic architecture.

Self-programmable, self-assembling two-dimensional genetic matter.

Putative two-dimensional coding systems can beconstructed from aqueous solutions of purine andpyrimidine nucleic acid bases evaporated at moderatetemperatures on the surfaces of inorganic solids. Theresultant structures are monolayers which are formedspontaneously by molecular self-assembly and they havebeen observed with molecular resolution by scanningtunnelling microscopy (STM). When formed fromsolutions of a single base, the monolayers of adenineand uracil have crystalline characteristics and theSTM images can be interpreted in terms of thegeometrical placement of planar arranged moleculesthat interact laterally by intermolecular hydrogenbonding. When formed from solutions containing amixture of adenine and uracil, the monolayers haveaperiodic structures. Small crystalline domainswithin these monolayers can be interpreted in terms ofthe single phase configurations of the molecules andthe remaining aperiodic structures can presumably beinterpreted, geometrically, in terms of the 21theoretically possible adenine-adenine, uracil-uraciland adenine-uracil hydrogen bonding interactions. Wepropose that combinatorial arrangements of planararranged purine and pyrimidine bases could provide thenecessary complexity to act as a primitive geneticmechanism and may have relevance to the origin of life.

Scanning tunneling microscopy of uracil monolayers self-assembled at the solid|liquid interface

Scanning tunneling microscopy has been performed on the 2,4-dioxopyrimidines, uracil and thymine, which self-assembled into monolayers on heated surfaces of highly oriented pyrolytic graphite and molybdenum disulfide. Our results suggest that the structures of these adsorbates, on both surfaces, are two-dimensional hydrogen-bonded networks with intermolecular configurations almost identical to those predicted by electrochemical studies of these compounds at the mercury|water interface and determined by X-ray crystallography of their respective three-dimensional solids.

Origins of life: a route to nanotechnology.

The origins of life and nanotechnology are two seemingly disparate areas of scientific investigation. However, the fundamental questions of lifes beginnings and the applied construction of a Drexlerian nanotechnology both share a similar problem; how did and how can self-reproducing molecular machines originate? Here we draw attention to the coincidence between nanotechnology and origins research with particular attention paid to the spontaneous adsorption and scanning tunneling microscopy investigation of purine and pyrimidine bases self-organized into monolayers, adsorbed to the surfaces of crystalline solids. These molecules which encode biological information in nucleic acids, can form supramolecular architectures exhibiting enantiomorphism with the complexity to store and encode putative protobiological information. We conclude that the application of nanotechnology to the investigation of lifes origins, and vice versa, could provide a viable route to an evolution-driven synthetic life.

Scanning Tunnelling Microscopy and Molecular Modelling of Xanthine Monolayers Self-assembled at the Solid-Liquid Interface: Relevance to the Origin of Life

The development of scanning tunnelling microscopy (STM) has allowed examination of inorganic crystalline surfaces and their interactions with organic adsorbates with unparalleled resolution. As a novel technique in origin of life studies, the application of STM is detailed with particular attention paid to the methods employed in the analysis of organic monolayer structures. STM imaging and molecular modelling of self-assembled monolayers of the purine base, xanthine, formed on the surfaces of graphite and molybdenum disulfide are presented as an example. The putative role of such structures in the origin of life is discussed.

Life before RNA.

The hypothesis that life originated and evolved from linear informational molecules capable of facilitating their own catalytic replication is deeply entrenched. However, widespread acceptance of this paradigm seems oblivious to a lack of direct experimental support. Here, we outline the fundamental objections to the de novo appearance of linear, self-replicating polymers and examine an alternative hypothesis of template-directed coding of peptide catalysts by adsorbed purine bases. The bases (which encode biological information in modern nucleic acids) spontaneously self-organize into two-dimensional molecular solids adsorbed to the uncharged surfaces of crystalline minerals; their molecular arrangement is specified by hydrogen bonding rules between adjacent molecules and can possess the aperiodic complexity to encode putative protobiological information. The persistence of such information through self-reproduction, together with the capacity of adsorbed bases to exhibit enantiomorphism and effect amino acid discrimination, would seem to provide the necessary machinery for a primitive genetic coding mechanism.